FC HDD vs SCSI HDD

[Oleg Mochkin]

What is main advantage FC disks over SCSI ?
Oleg.

[Karthik S S]

With FC harddisks you get better througput. Also the number of devices than can be connected to a FC Loop (128 devices) /fabric (in millions) is far more compared to SCSI (max 15 devices).

Also refer,
http://www.storagereview.com/guide2000/ref/hdd/if/sfFCAL.html

-Karthik S S

[Wayne Rippy]

Agree, typically you find faster read/writes, and you are able to have more disks in a set.

However, I would caution that if you are looking to purchase a new "SAN" that you look at the overall environment. Just because the disks are capable, and are able doesn't mean they will read or write faster. Alot of that depends on through put from the application on the server, through the HBA's, to the controller cache. Then the 'ack' given back to the 'requestor' or server sending the data, and finally a destage of cach to disk.

The performance of FC disks is most notable with small block data in non-sequential writes (i.e. causing cache to destage to disk constantly).


Keeping consistant with the forum, I will refrain from speaking of 'other architecture' from other vendors. In general the architecture of HP/Compaq SANS is the same. So this 'scenerio' of writing small block data over and over non-sequentially is really the only place a performance increase might be seen.

[Hein van den Heuvel]

The FC speeds can be a lot higher
(1Gbit/2Gbit) over longer distances with no electrical interference.

The high speed wide copper scsi only accepts relatively short distances, the cables are short, heavy and thick. You can get electtricl connection problems (ground loops) and can receive (and send) electrical interference.

fwiw,
Hein.

[Uwe Zessin]

Today's FC disks have dual-port active/active connections. That is nothing new - I already have seen dual-ported disks in the eighties and I won't be surprised if such disks have existed for a much much longer time.

Of course, that is highly needed. If one device blocks a parallel SCSI bus (15 devices) or one FC-loop (on the EVA up to 56 devices [1]) - the game IS OVER on that communications channel!

[1] Any EVA with more then 56 disks (=4 disk drive enclosures) should have been equipped with loop switches that provide better fault isolation. In case such a switch fails, you still have a second switch on the other loop.